The Move Entity Down command is used to decrease the elevation of an entity on the drawing.
To move an entity down, go to
Ribbon: DM HVAC->Drafting-> 
Move Entity Down
Pulldown Menu: DM HVAC->Drafting Tools->Elevations->Move Entity Down
You will be prompted to select the entities to be moved down.
Select entities to move:
You will then be prompted to specify the distance the entities are to be moved.
Enter distance to move up:
Their elevation will be decreased by the specified distance.